Contrast is the amount of separation between dark and light tones, whereas density refers to the opacity of exposed silver in the negative. A dense negative is effectively a thicker negative which requires more exposure to enlarge, usually resulting in increased apparent grain. Overexposed or overdeveloped negatives have excessive density, whereas underexposed or underdeveloped negatives lack density. Density often affects contrast. For instance, an underdeveloped negative will almost always be low in contrast and low in density, but the correlation depends on a number of factors including film type, developer type and whether the fault is due to over/under exposure or development.

kcf wrote:Can anyone explain what the difference between contrast and density is? I know pushing increases density rather than contrast, but what does this mean?

Pushing does NOT increase density, only contrast! Density refers to the "blocking power" of the negative, i.e., how much light it blocks compared to nothing. Contrast refers to the difference between the thinnest and densest areas of the negative. Increasing exposure tends to increase density overall; increasing development tends to increase density in the denser areas only. That is why pushing does not work.

Ornello, people like that pushy look, though. Pushing gives an high-contrast look with little mid-tone and people think that's cool, especially when they're starting out shooting black and white film.

Also, if you shoot in low light, you can get negatives that are so low in contrast they're virtually unreadable. Pushing gives you a certain readability, even if it reduces gray scale. You can see what's going on easily and there's a certain level of impact you wouldn't otherwise get. I agree you're not increasing the ISO of the film. But you're still altering the negative in such a way as to create readability in a neg that would otherwise be unreadable.

I think people are drawn to the stark, grainy edginess of the pushy look. They like the transformation rendered by pushing. It creates a negative (emotionally), down look. It creates a sense of grittiness and maybe realism. You could say it gives pictures a sense of abstraction and reduction to lithographic essentials.

That's not an argument in favor of pushing! Just thinking aloud since so many posts are about pushing. This question grew out of a post about pushing on another site.

Ornello wrote: Pushing does NOT increase density, only contrast! Density refers to the "blocking power" of the negative, i.e., how much light it blocks compared to nothing. Contrast refers to the difference between the thinnest and densest areas of the negative. Increasing exposure tends to increase density overall; increasing development tends to increase density in the denser areas only. That is why pushing does not work.

I was out yesterday shooting up a roll of Konica Infrared that expired in 2005. It was the last of the rolls I bought a few years ago when I heard that it had been discontinued. I have a 9 more rolls that I bought off of eBay in the spring, but that's immaterial other than to make the point that I'm really careful with this film. Each frame is prescious. Needless to say, I made a mistake when exposing it yesterday. I used a red 29 filter insteaad of my usual red 25. There is a 1 stop difference between the two. I forgot to calculate that in. I decided to push process. I used PMK Pyro because it has a compensating effect, which retards the highlights while bringing out the shadows. I increased development time by 50%, and hoped for the best. When I removed the film from the developing reel, I laughed like a mad scientist. The negatives were perfect. The results can be seen on my Flickr page: St John's Bridge numbers 3, 4, and 5. Sometimes push processing does indeed work.